Starch xanthate derivatives used in papermaking

ABSTRACT

A METHOD OF PREPARING PAPER IS DISCLOSED WHICH INCLUDES THE STEP OF ADDING TO THE PAPER PULP THE PRODUCTS OF THE REACTION OF STARCH XANTHATE WITH EITHER AN ALKYL DIGLYCIDAL ETHER ORAN ALKYL DIEPOXIDE TO THUS INCREASE, BURST, WET AND DRY STRENGTH AND FOLD ENDURANCE OF THE PAPER. THIS REACTION MAY TAKE PLACE EX OR IN SITU.

United States Patent 3,730,829 STARCH XANTHATE DERIVATIVES USED IN PAPERMAKING George G. Maher, Dunlap, lll., assignor to the United States of America as represented by the Secretary of Agriculture No Drawing. Filed Oct. 18, 1971, Ser. No. 190,319

Int. Cl. D21h 3/28 U.S. Cl. 162-175 6 Claims ABSTRACT OF THE DISCLOSURE A method of preparing paper is disclosed which includes the step of adding to the paper pulp the products of the reaction of starch xanthate with either an alkyl diglycidal ether or an alkyl diepoxide to thus increase, burst, wet and dry strength and fold endurance of the paper. This reaction may take place ex or in situ.

A nonexclusive, irrevocable, royalty-free license in the invention herein described, throughout the world for all purposes of the United States Government, with the power to grant sublicenses for such purposes, is hereby granted to the Government of the United States of America.

BACKGROUND OF THE INVENTION This invention relates to the preparation of molded articles and films having properties which vary from hard and brittle to soft and pliable. More specifically, the invention relates to products prepared from cros'slinked starch xanthate. Reactions which crosslink carbohydrates, especially polysaccharides, through their hydroxy groups are fairly well known. Crosslinked dextran, molecular sieves, and crease-resistant cotton cellulose fibers are among the more important products of this type. However, the amount of crosslinking or the degree of substitution (D.S.) attained in these products is quite low. Furthermore, to obtain the desired results in preparing the abovementioned products, it is often necessary to use various combinations of organic solvents, catalysts, emulsifiers, or suspension stabilizers (when water is present), application of heat, and curing of products.

Crosslinking of sodium starch xanthate has been achieved by reaction with polyethylenimine, polyacrolein, and low molecular weight polyamines. Many of the gels formed in these reactions were fiuid, but some were rigid enough to support themselves without flowing when the reaction vessel was inverted. However, these rigid gels were not firm enough to maintain the shape of a mold when removed therefrom and when dried, they resulted in gummy masses. Gels prepared from polyacrolein and sodium starch xanthate (D.S. 0.22-4.44) were exceptional in that they dried to hard, brittle, glasslike products. In the prior art teachings of the above reactions, it is indicated that the reactive moieties of the crosslinking agents react only with xanthate groups in sodium starch xanthate and that, while a long chain between cros'slinking sites is not always necessary for gel formation, the molecular size of the connecting bridge should be considerable to impart insolubility to the product.

I discovered that hard products, such as molded articles and films, which retain the shape of a mold were formed when sodium starch xanthate having a xanthate D8. of from about 0.05 to about 0.60 was reacted with an excess of an alkyl diglycidyl ether such as 1,4-butanediol diglycidyl ether or an alkyl diepoxide such as butadiene diexpoxide in an alkaline aqueous medium. The excess of the diepoxides was from about 2 to about times the stoichiometric amount of one epoxide group per xanthate group in the sodium starch xanthate starting material. Plasticizer's were added in amounts of 0 to 200 percent of the dry weight of the sodium starch xanthate. The reaction Was conducted in a mold for a time sutficient to allow formation of a solid mass. This solid mass was removed from the mold and allowed to dry. In some instances dyes or fillers were added to the reaction mixture in suificient quantity to impart color to the molded article's. Materials such as brom cresol purple, carbon black, potassium permanganate, Sudan black, Congo red, halopont blue, methylene blue, brom thymol blue, cresol red, or any other compatible compound which can impart color can be used in this manner.

The reaction of sodium starch xanthate with diepoxides is homogenous, very rapid (at least at the start), requires no heating or catalyst, and takes place in a simple, alkaline water medium. The crosslinked products first form opaque, gel-like masses that coalesce to solids which, as they form, come out of solution in one piece or mass, and the residual liquid medium quickly exudes or weeps from the solids. The solid masses dry to form materials which have properties that vary from soft and flexible to tough and nonflexible to brittle depending on the ratio of xanthate to diepoxide. Molded products retain sharp clear letters when the reaction takes place in a mold having embossed lettering. At early stages of formation, the instant products could lend themselves to compression molding. Colors of nondyed products range from white to yellow depending on the amount of diepoxide reacted. The products do not melt, but they do burn freely. They are essentially insoluble in such solvents as benzene, toluene, hexane, dioxane, methyl cellosolve, ethyl ether, ethanol, butanediol, acetone, glacial acetic acid, pyridine, chloroform, carbon tetrachloride, and dimethyl sulfoxide.

The simple molding characteristics of the instant products make them especially useful for casting and molding small pieces, sealants, films, adhering films, reinforced fiber cloths and mats, protective coverings of films as reinforced film fiber, plain or reinforced gaskets, stretchable gaskets, and pliable fillers.

I have further discovered that paper having increased burst, wet and dry strength, and fold endurance, results from first reacting sodium starch xanthate having a xanthate D5. of from about 0.1 to about 0.6 with an excess of an alkyl diglycidyl ether or an alkyl diepoxide, the excess being from 2 to 5 times the stoichiometric amount of one epoxide group per xanthate group in the sodium starch xanthate; then adding the resulting reaction mixture to a papermakers pulp suspension in amounts that result in levels of addition of from about 2.5 to 10 percent based on total weights of reactants and dry pulp; then allowing the resulting pulp mixture to stand from about 0.5 to about 18 hours; forming water-laid paper from the pulp mixture; and finally drying the paper.

Paper having essentially the same properties as above can be prepared by separately adding the same quantities of reactants to the papermakers pulp, allowing the mixture to stand from 0.5 to 18 hours, and finishing the process in the same manner.

DETAILED DESCRIPTION OF THE INVENTION The cros'slinking reaction of sodium starch xanthate with an alkyl diepoxide is the basic element in this invention. Therefore, for the purpose of the invention, conducting the reaction in a mold to form a molded article is considered to be equivalent to conducting the reaction on a fiat surface to form a film.

Sodium starch xanthate solutions (pH 11) having a 10-13 percent dry substance content were prepared as described by Swanson et al., Ind. Eng. Chem, Prod. Res. Develop. 3:22 (1964) and Doane et al., Die Stiirke 17:77 (1965). Each solution was used within 12 weeks after preparation (see Example 8, infra) since there is some decomposition and loss of D.S. after that time. The Xanthate solutions were analyzed for dry substance starch and for xanthate groups from which D.S. and dry substance starch xanthate content based on the anhydrogluco'se unit (AGU) were calculated as described by Doane et al., supra.

Commercially obtained diepoxide crosslinking agents without further purification or modification were reacted with sodium starch xanthate. The following types of diepoxide compounds are considered suitable for use in the instant invention:

butadiene diepoxide. Any alkyl diepoxide of the above types having unsubstituted carbon or carbon-oxygen chains of from -8 units between the epoxide rings is considered to be equivalent to the compounds described above.

The stoichiometric reaction of sodium starch Xanthate with a diepoxide is envisioned as follows:

H D.S. 2

Reactants Sodium starch xanthate, D.S.

4 hrs. 76 hrs S-ratio 1 2 28 hrs. 52 hrs.

mum-wrote 1 Ratio of epoxide groups to sodium xanthate group.

2 Diepoxide, 1,4-butanediol diglycidyl ether.

Usually, when the gels attain viscosities over 10,000 cp., the spindle of the viscometer creates a hole or crack in the gel that does not close after the spindle is removed making further viscosity measurements useless.

Gel formation is a good indicator of crosslinking and reaction progress. Another such indicator is the disappearance of the yellow color, typical of the sodium starch Xanthate solution after the alkyl diepoxides are added. The reactions were terminated at various times by pouring the reaction mixture into 95 percent ethanol to form a solid precipitate which was then analyzed for sulfur content by the method of White, Microchim. Acta, 807 (1962). Infrared (IR) absorption spectra were obtained on Nujol mulls between NaCl discs. The reactions shown in Table 2 were conducted in closed vials in order to more easily measure viscosity and to form products which could be manipulated for analysis. Reaction times were determined by sulfur analysis and ultraviolet absorption analysis of the supernatant reaction solution. Reactions were considered to be ended when all of the Xanthate moieties in the starting material were reacted. No free sulfur was 'found in the reaction medium.

1 Calculated from sulfur analysis.

2 Ratio of epoxide groups per xanthate group. 8 Diepoxide, 1,4-butanediol diglycidyl ether. 4 Determined by IR at 6.75 n.

where R=starch, R'=-CH -0CH CH or {CH -l where x=0-4, and D.S.:degree of substitution of sodium xanthate on the starch. According to the above stoichiometry, one sodium xanthate group reacts with one epoxide group. The ratio of epoxide groups to xanthate groups will be known herein as the Sratio.

Attempts were made to follow the reactions by measuring viscosity development with a Brookfield viscometer, but this proved to be diflicult since in most case the reaction quickly produced too strong gels and solid precipitates. However, a few viscosity measurements are shown in Table 1.

As indicated in the table, the gelling rate and extent are dependent on the D.S. of the starch xanthate, being the least with the low D.S. and increasing as the D.S. increases. Gelling also depends upon the amount of epoxide used. Reactions with the starting materials having S-ratios of 1-1.5 did not result in appreciable gelling or viscosity increases at all D.S. levels and over reaction times extended to several days. Reaction products described in Table 2 as being firm gels when left overnight in their reaction vials, harden to form solid handleable masses. A handleable mass or product is defined herein as having the ability to be removed from its container,

without significant distortion. Those products described as being soft gels harden to form solid handleable films when their respective reactions are performed as described in the examples, infra. Times sufficient for handleable products to form depend on the D5. level of the sodium starch xanthate and the amounts of alkyl diepoxide added. These times are usually from 8 to 72 hours. Prior art indicates that alkyl diepoxides will not react with starch except in the presence of catalyst or relatively high pI-Is, nor will they polymerize under the reaction conditions of the instant method. It was unexpected, therefore, when I discovered that alkyl diepoxides reacted with sodium starch xanthate in more than the supposed stoichiometric quantities (i.e., S-ratios greater than 1). The reactions were conducted at room temperature (about 25 C.) in the light in an aqueous medium having a pH of about 11.

Sulfur analysis of products obtained from reaction mixtures containing a twofold excess of epoxide groups indicates that 2 moles of epoxide groups (or mole of diepoxide) per xanthate group had reacted. Similar reaction media containing a fivefold excess of epoxide groups produced a crosslinked material that contained only 3 moles of epoxide groups per mole of xanthate group. This limitation of epoxide addition indicates that the diepoxides are not polymerizing. Perhaps the presence of the xanthate group on the starch somehow activates starch hydroxyls, and the excess epoxide groups are reacting with these activated functional groups.

The existence of a carbonyl band at 5.75 1. in the IR spectra of the product obtained from the reaction of 1,4- butanediol diglycidyl ether with sodium starch xanthate is evidence that the epoxide has attached to a xanthate group which is on a secondary carbon adjacent to a carbon containing a hydroxyl group. Similar structures are known to spontaneously rearrange so that their IR spectra show a peak at 575 Reactions of sodium starch xanthates having low D.S. levels with alkyl diepoxides cast on a glass surface result in products which are thin, smooth, brittle, and clear. As the xanthate D8. is increased, the resulting films become thicker, rougher, more opaque, and tougher. The effect of adding plasticizers such as glycerol, 1,4-butanediol, dipropylene glycol, and ethylene glycol to reaction mixtures containing the prescribed reactants in various combinations of xanthate D.S. levels and S-ratios is to in crease the strength, flexibility, and elasticity of the products. Films were also cast which incorporated cotton cheesecloth, and random-piled and nonwoven fiber glass cloth, and woven fiber glass cloth. These showed a very significant synergistic effect on the strength of the resulting products, which in some cases were 20 to 50 times stronger then either the film or the cloth alone.

There is no preferred xanthate D.S. level, S-ratio, or amount of plasticizer within the operable limits of the instant method. It is my belief that from the procedures and discussion herein disclosed those skilled in the art can, without excessive amounts of experimentation, determine the reaction parameters and combination of reactants and additives which would result in products having the most useful physical properties for their purposes.

The reaction described above between sodium starch xanthate and alkyl diepoxides, when incorporated into the production of paper, results in products having increased wet and dry strength. However, in this application, the reaction is conducted under conditions that prevent formation of solid masses. This can be accomplished by using starch derivatives having low to medium xanthate D.S. levels (e.g., 0.1 to 0.2) and diepoxides in low S- ratios (e.g., about 2), by using short reaction times with materials having higher D.S. levels, by conducting the reaction in dilute solutions or by conducting the entire reaction in the papermakers pulp suspension. For example, when a starch derivative having a xanthate D-.S. of about 0.1 was reacted with 2 times the stoichiometric amount of 1,4-butanediol diglycidyl ether for up to 76 hours, the

product remained a soft gel. A similar reaction conducted for 5 minutes ex situ (i.e., outside the paper-pulp slurry) and 2 hours in situ (i.e., in the paper-pulp slurry) resulted in a product which had extraordinary resistance to the MIT fold test (see Example 24, infra). Reactions of sodium starch xanthates having D.S. levels of up to 0.6, with diepoxides in S-ratios of about 3, conducted in dilute solutions do not gel but form turbid suspension. If the reaction medium is sufficiently dilute (see Example 20, infra), solid masses do not form upon standing for as long as 55 hours.

In one of the two preferred papermaking procedures, sodium starch xanthate and an alkyl diepoxide in preferred S-ratios of about 3 are reacted ex situ in an aqueous medium for about 5 minutes and reacted in situ for from 0.5 to 18 hours. In a reaction time of 0.5 hour essentially all the xanthate moieties have reacted as is indicated in Table 2, supra. However, Example 24, series 2, indicates reaction times of up to 6 hours result in some increase in paper strength. Levels of addition for the reactants is from 2.5 to 25 percent based on the dry weight of the paper pulp which, in the examples (infra), is an' unbleached, softwood, sulfate papermakers pulp containing percent by weight moisture. The moisture was taken into account in calculating levels of addition. When the sodium starch xanthate D.S. level is high (about 0.6), a 2.5 percent level of addition is sufficient. At lower xanthate D.S. levels increasing the level of addition significantly increases the paper products wet strength and resistance to the MIT fold test.

The second preferred procedure for producing paper is one in which the entire reaction of sodium starch xanthate with alkyl diepoxides is conducted in situ. Reactants in the same amounts as described above added separately to a papermakers pulp suspension and allowed to react for the same lengths of time resulted in products of superior strength to those prepared by procedures described in the prior art, using commercial paper strength additives. Example 23, infra, indicates that, when the alkyl diepoxides are added first and sodium starch xanthate immediately after, there is a significant increase in retention over that obtained when the reverse procedure is used. All parameters other than those described above for the crosslinking reaction are considered to be those normally used in the production of paper.

The following examples are intended only to further illustrate the invention which is defined only by the claims. Casting as Film:

EXAMPLE 1 Reaction mixtures of the following three compositions were made, the first part (a) detailing the procedure.

(a) To 45 ml. of Water were added 0.9 ml. (0.979 g., 3 times stoichiometric amount) of 1,4-butanediol diglyci dyl ether and 6 ml. (7.56 g.) of glycerol. After mixing, 45 g. of an 8.68 percent, 0.15 D.S. sodium starch xanthate solution of pH 11 to 12 (made from ordinary pearl corn starch) was weighed in quickly, and rapid mixing was continued until the mixture began to thicken or develop turbidity (a matter of a few minutes).

(b) 45 ml. of water, 1.8 ml. (1.958 g.) of 1,4-butanedioldiglycidyl ether 6 ml. (7.56 g.) of glycerol, and 45 g. of a 10.10 percent 0.25 D.S. sodium starch xanthate solution.

(c) 45 ml. of water, 4.0 ml. (4.351 g.) of Araldite RD-2, 6 ml. (7.56 g.) of glycerol, and 45 g. of a 13.74 percent 0.51 D.S. sodium starch xanthate solution.

After the thickening point was reached, the mixtures were poured into a mm. (5.75 in.) diameter glass Petri dish which was covered and set at ambient room conditions (25 C.) for 24 or 72 hours. The liquid which exuded was measured. The separated, solid disk that had formed was rinsed with water and dried on a glass plate in the room air, turning occasionally on the plate which had been coated lightly with silicone fluid having a viscosity of 50 centistokes at 25 C. for several days.

The entire foregoing experiment was repeated with the elimination of glycerol in the recipes.

The principal observations are tabulated below:

Exuded Time liquid D.S (hr) Glycerol (ml) Comments on film 25 Thieilg, rough, firm, shriveled, opaque pad. 45 o. 35 Thirigr, fairly smooth, pliable, opaque pad. 45 o. 13 Thicilg, brittle, shrivelcd, opaque film. 22 0. 19 Thicllg, smooth, pliable, opaque film.

8 o. Thin, smooth, brittle, cracked, clear llhn. 0 o. 0 Thin, smooth, pliable, clear film.

I These casts from 0.15 D.S. xanthates do not separate from the dish Walls but can be cut away. The clear films are yellow but transparent.

E MPLE 2 t i B ki t t ii El t 1011 a rca n s ren as To 45 ml. port1ons of water added 3, 4, or 5 ml. (3.78, Glycerol; break factogr at 5, modulus 5.04, or 6.30 g.) of glycerol and 0.34 to 1.70 ml. (0.369 (percent) (p n (lb/in.) (p.s.1.) .s.i.) to 1.845 g.) of 1,4-butanediol diglycidyl ether in multiples 73 46 383 23,411 of 0.34 ml. Then weighed in and mixed rapidly 45 g. of a a; g is;

10.93 percent 0.13 D.S. sodium starch xanthate solution, giving reaction mixtures with 1 to 5 times the stoichiometric amount of the ether. The mixtures were cast in the covered Petri dish for 3 days and then processed as in the preceding experiment.

The dried films were cut into strips and tested for tensile properties according to ASTM Designation D 882-64 T for thin plastic sheeting after equilibrating for 48 hours or more according to ASTM Designation D 618. An Instron testing machine was used. The following table summarizes the results:

Elenga- Tensile tion at Breaking strength Elastic Glycerol 2 break factor at break modulus S-ratio 1 (percent) (percent) (lb./n.) (p.s.i.) (p.s.i.)

76 N o strength in wet cast, not handleable 76 11 471 28, 389 76 60 10 449 22,728 76 11 12 535 27,577 76 72 5 232 13,212 102 132 5 154. 1,493 102 134 4 155 1,949 128 91 1 33 469 128 60 1 156 1 Ratio of epoxide groups per xanthate groups, or excess of epoxide groups based on stoichiometric reaction.

2 As percent of sodium starch xanthate dry Welght.

Those films made with 100 percent or more of glycerol are tacky, the tack increasing with the amount of glycerol, and adhere to glass, metal, and wood or paper fairly well.

EXAMPLE 3 To 45 ml. portions of water added 3 ml. (3.78 g.) of glycerol and increments of 1,4-butaned1'ol diglycidyl ether to provide varying S-ratios. Then 45 g. of an 11.5 percent 0.25 D.S. sodium starch xanthate were weighed in, mixing accomplished rapidly, and the mixture cast in the Petri 1 See table, Example 2. 9 As percent of sodium starch xanthate dry weght.

EXAMPLE 4 When casts, made in accord with recipes as in Examples 2 and 3 which contained 4 ml. of glycerol, were put on -inch mesh screens rather than glass to dry after being removed from the dish mold and washed, the resulting films were very pliable, tacky, clear, yellow, smooth on one side, and cleanly imprinted with the mesh of the screen on the other side, giving a nonslip surface. Shrinkage on drying was very slight because of the holding power of the coarse screen on the film, but the films were easily peeled from the screen. Tensile strength tests on the ribbed film revealed no significant strength variations from the unribbed films.

Attempts to cure and dry casts from 0.50 D.S. Xanthates on the screen were not as successful as the sheet was rather thick (over 1 mm.) and opaque and although pliable tended to disfigure some in the late stage of drymg.

EXAMPLE 5' Casting mixtures were made in accord with the practices of Examples 2 and 3 using varying amounts of glycerol and varying S-ratios of the epoxide, but using 0.14 and 0.22 D.S. sodium starch xanthate made from a different corn starch than the one used to make the 0.13 and 0.25 D.S. xanthates of Examples 2 and 3. These mixtures were cast in the Petri dish molds in which a full circle of cheesecloth had been placed. Casts were also made without cheesecloth. After the due processing, the films were rather clear and the cheesecloth was quite evenly impregnated in continuous appearance with no voids or flaws. The composites were tested for tensile properties on the Instron machine but an elastic modulus calculation was not operable because of the dish. Subsequent processing and testing as in Example 2 manner 1n whlch the test strips broke without much provided the data following 1n Column 8. elongation.

Elonga- Tensile tion Break strength Glycerol at break factor at break D.S. S-ratio (percent) (percent) (lb/in.) (p.s.i) Appearance 2 None 175 1.1 48 2 76 38 6. 5 354 Flexible, no tack. 0.14..- 3 76 30 13. 6 670 Do.

3 102 28 10. 8 500 Very flexible, some tack. 3 128 35 11.7 543 Very flexible, most tack. 5 None 161 1.2 71 2 69 32 10.9 710 Opaque, flexible. 0.22 6 69 20 14. 3 845 D0. 5 02 29 6.8 444 D0. 5 24 7.3 474 Do.

1 See table, Example 2.

2 As percent of the sodium starch xanthate dry Weight.

3 No cheesecloth in these.

4 Only a half of the normal reaction mixture was cast at this D.S.

These data illustrate a synergistic effect of combination of cheesecloth and derivative as the cheesecloth alone has a break factor of 7 to 8 pounds per inch.

EXAMPLE 6 1 EXAMPLE 9 (A) To 45 ml. of water was added a 3 times stoichiometric amount of the diepoxide of Example 1. Then added 3 ml. (3.78 g.) of glycerol, 3 ml. (2.88 g.) of

To 45 m1 of Water were added 3 (378 of 5 epoxidized butyl linseed oil with an oxirane oxygen conglycerol and 2 or 3 times the stoichiometric amount of m of T or 3 Of an epoxldlzed soybean 011 the diepoxide of Example Then 45 g. portions of with an oxirane oxygen content of about 7.0%. Next 45 either an 11.23 percent 0.05 D.S. sodium starch xanthate, a Percent Sodlum stareh Xanthate or a 10.94 percent 0.13 D.S. sodium starch xanthate, 10 sohmon or PerFent stareh or an 11.24 percent 0.25 D.S. sodium starch xanthate, Xanthate solutlon was Welghed and mnfed The or a 13.21 percent 0.54 D.S. sodium starch xanthate tufes were east and ee- After drylng, the only solution made from the same Starch as used in the pliable films were those containing glycerol. All the others xanthate preparations of Example 5 were weighed in were bmfle, Cracked, and 8- and mixing accomplished. The mixtures were cast in the 15 It noted that the epOXldlzed butyl 11need 011 With Petri dishes which contained a full-cut circle of a an oXlfal'lfi Y Content of sefimed t0 F random-piled, nonwoven fiber glass cloth or a fiat cloth Pt faster reactl'ofl f t tufbldlty development d1 1f1ng of multifilament, fiber glass strips, about -inch wide, mlXlng, and the CPOXIdIZed ybean oil w1th an oxlrane woven loosely together at nine strips per inch, 7.5 ounces. OXYgeII Content about 7 eemed to diminish the Casts were also made without fiber glass incorporation. 20 amount of shrinkage during curing.

Glycerol was added to all reaction mixtures at ca. 70 (B) To 4 ml. of water added 1 ml. (1.09 g.) of the percent of the dry weight of sodium starch xanthate. diepoxide of Example 1. The amount of diepoxide is 3 Elonga- Tensile tion at Break strength Elastic break factor at break modulus Fiber glass D.S. Saatio (percent) (lb/in.) (p.s.i.) (p.s.i.)

1 See table, Example 2.

2 Only a halt recipe mixture was cast.

After due processing the composite films were tested times the stoichiometric amount needed for the amount for strength properties. Again a synergistic effect in of xanthate to be used. Next 3 ml. of one of the following the reinforcement was noted. agents was added as plasticizer: (1) 1,4-butanediol, (2)

EXAMPLE 7 dipropylene glycol, (3) 1,2,6-hexanetriol, (4) triethylene glycol, and (5) ethylene glycol.

T0 1111. Of wefeadeed 8-) of 45 After mixing, 45 g. of a 10.12 percent 0.12 D.S. soy and 3 tlmes the $t1eh1metnc amunt of the dium starch xanthate solution was added. The mixture dlepoxlde of Example T 45 Portlons of the was rapidly and well stirred until signs of thickening ap- DS or the sodlum stal'ch Xanthates Q Exam peared and then poured into the Petri dish to cast. After ple 6 were m1xed 1n and casts for film for were being in the cast for 18 hours the soft, solid sheets were {nade the Fem The castmgs were Processed floated out of the dishes in water, rinsed gently, and into dried films as before and these were tested for then processed through drying as strengtepmpertles after stormg at room condltlons for All cast sheets were easily removable and handleable. Vaned tune Penods After drying for about 4 days, the films with the butanediol or dipropylene glycol were somewhat intermediate T 1 5 5 in pliability and could be broken on sharp bending. Films Storage Elongation Break -33221? Elastic With hexanetriol or triethylene glycol on the other hand time at break 1 gaqtoi at break modulus were very brittle and cracked upon slight bending. They (Vt (Demem) also had a white surface bloom. None of the films had 2 3 1 g-g $91 an oily feel or surface as did those: of Example 9A which 12 172 m 3 505 contained Epoxol of Flexol. %g is? 2 Only the film made with ethylene glycol had a pliability 16 230 1:9 439 approachmg that of film made with glycerol as plasticizer. After about 3 weeks of drying at room conditions even f h d i if fii l sfiffifitml xfifitit at ca 70 pement 0 t e the film w1th ethylene glycol becomes rather brittle, al-

65 though remaining without bloom, whereas films with EXAMPLE 8 glycerol seem to remain flexible indefinitely.

A study of the effect of the age of the sodium starch EXAMPLE 110 xanthate solution on film strength properties was made To 45 1 f te dd d 3 1, (3,78 f glygerol, concurrent with Example 7, using the 0.05 D.S- Stflrch Then added one of the following quantities of diepoxide,

derivative in the same recipe mixture as in Example 7. The strength test results on the films produced showed no effects due to the aging of the xanthate solution through the time steps 1, 7, and 12 weeks. The individual strength values were in very excellent agreement with those in the table of Example 7 relating to the 0.05 D.S. xanthate.

each representing a 3 times stoichiometric amount-0.82 ml. (0.89 g.) of 1,4-butanediol diglycidyl ether, 0.34 ml. (0.38 g.) of butadiene diepoxide or 0.81 ml. (0.90 g.) of glycerol diglycidyl ether. Forty-five g. of a 10.46 percent 0.11 D.S. sodium starch xanthate solution was weighed in and the mixtures were cast.

The mixture made with glycerol diglycidyl ether did not result in the formation of a solid entity and evapo ration of liquid left a gummy deposit. The solid casts were processed, dried, and tested.

When this procedure was repeated with a 3 times stoichiometric amount of the diepoxide in reaction with 0.12 D.S. or 0.24 D.S. sodium starch xanthate in place of 0.44 D.S., the casts from the lowest D.S. xanthate could not be Tensile l Glycerol as plasticizer at 80 percent of dry weight sodium starch xanthate.

EXAMPLE 1 1 To 45 ml. portions of water added 3 ml. (3.78 g.) of glycerol. Then added 1,4-butanediol diglycidyl ether in multiples of 0.25 ml. increments starting with 0.50 ml. to provide mixtures with 2, 3, 4, and times the stoichiometric amount of the ether. Next 45 g. of a 9.48 percent 0.11 D.S. sodium starch xanthate solution made from a high-amylose content corn starch was weighed in and the mixtures were cast in the Petri dishes. After the usual processing, the strength character of the films was determined. It was noted that the films from the high amylose starch were about twice as thick as those from ordinary corn starch.

Elonga- Tensile tion at Break strength Elastic Glycerol 2 break factor at break modulus S-ratio 1 (percent) (percent) (lb./in.) (p.s.i.) (p.s.i.)

2 90 No strength in wet east, not handleable 3 90 70 6. 8 123 901 4 90 113 5.5 97 1, 380 5 90 310 6. 7 124 1, 860

1 See table, Example 2. As percent of dry weight sodium hlgh-amylosestarch xanthate.

To 45 ml. portions of water added 3 or 4 ml. of glycerol. Then added 1.06 ml. of the above epoxide to provide mixtures with 3 times the stoichiometric amount of epoxide. Next 45 g. of a 10.30 percent 0.23 D.S. sodium highamylose-starch xanthate solution was weighed in, mixed, and the film castings made, etc.

To ml. of water was added 1.14 ml. (1.24 g., 3 times the stoichiometric amount) of 1,4-butanediol diglycidyl ether. Then quickly 15 g. of a 12.69 percent 0.44 D.S. sodium starch xanthate solution of pH 11.5 to 12 (made from ordinary pearl corn starch was weighed in and the mixture was rapidly stirred until it showed signs of thickening and turbidity, a matter of just a few minutes. At this point the mixture was poured into a mold: (l) a plastic box with embossed letters, (2) a glass tube, or (3) a cup making mold. The molds were allowed to set overnight at about C. or room temperature. Inspection of the molds showed a solid, yellowish mass in the shape of the mold, separated from surfaces of the mold, and surrounded by exuded liquid. The solid masses were easily removed from the molds, washed with water, and dried several hours.

When this procedure was repeated using a stoichiometric or twice stoichiometric amount of the epoxide, unhandleable casts were obtained, respectively being a mushy suspension and a soft gel.

removed from the molds, having exuded essentially no liquid; and those from the intermediate D.S. xanthate could be removed only with difficulty, having exuded only a small amount of liquid.

When this procedure was repeated every 2 days with a 0.42 D.S. xanthate over a 2-week period, no detectable dilferences in the casting characteristics were noted, indicating no effect due to xanthate age within this time period.

EXAMPLE 13 To 15 ml. of water was added 1 ml. (1.26 g.) or 2 ml. (2.52 g.) of glycerol or 1 ml. (0.96 g.) or 2 ml. (1.92 g.) of epoxidized butyl linseed oil with an oxirane oxygen content of 7.58.0%. Then added 1.31 ml. (1.43 g., 3 times the stoichiometric amount) of 1,4-butanediol diglycidyl ether. In the manner of Example 12, 15 g. of a 13.49 percent sodium starch xanthate solution (0.49 D.S.) was Weighed in and the mixture processed as in Example 12. The casting was in a cup mold. The casts were removed, washed, and subjected to drying as follows. One of each composition was placed on a wire screen to dry in the ambient room conditions and one of each composition was placed on a wire screen to dry in a desiccator over P 0 under vacuum at ambient room conditions. Every 48 hours the casts were weighed until essentially constant weight was reached in 8 days. The characteristics of the dried casts related to the plasticizer use as follows:

Plasticizer retention, Plasticizer Trimness percent 1 ml. glycerol 2d softest 72 2 ml. glycerol Softest 69 1 m1. epoxidized butyl linseed Hardest, oily surface oil with an oxirane oxygen content of 7. 58. 0%. 2 ml. epoxidized butyl linseed 3d softest, oily surface"..- 100 oil with an oxirane oxygen content of 7. 5-8. 0%

To 10 ml. of water added 1.28 ml. (1.395 g., 3 times stoichiometric amount) of 1,4-butanediol diglycidyl ether. Then added small portions of the dye materials listed below, all except the carbon black dissolving. Next, in the manner of Example 12, 15 g. of 12.57 percent sodium starch xanthate solution (0.52 D.S.) was added and the stirred mixtures were cast in a small funnel. The casts were removed, washed, and dried in the ambient room air. The high D.S. of the xanthate here and the lesser amount of water used results in more shrinkage and distortion than occurs with a ca. 0.40 D.S. xanthate. All gave acceptable products with the desired color.

13 (1) Brom cresol purple (2) Carbon black (3) Potassium permanganate (4) Sudan black B (5) Congo red (6) None (7) Halopont blue (8) Methylene blue (9) Brom thymol blue (10) Cresol red When the foregoing recipe was altered to contain ml. of water nad the casts were made in the cup mold or the lettered box mold, the dried casts were evenly dried and colored with sharp detail.

EXAMPLE 15 To 15 ml. of water added 1.32 ml. (1.440 g., 3 times the stoichiometric amount) of 1,4-butanedi0l diglycidyl ether, and 1.61 g. of either calcium carbonate (125 mesh) or carbon black. Mixed well and weighed in 15 g. of an 11.92 percent sodium starch xanthate solution (0.58 D.S.) quickly, mixed further until viscosity development hecame apparent and then cast in the cup mold or the lettered box mold. The casts were removed, washed, and dried. The cup casts were somewhat pliable, with little distortion and shrinkage. The lettered box cast with carbon had little shrinkage and the lettering was quite clear and sharp. However, the box cast with carbonate was not good, and a blooming tendency of the carbonate destroyed the lettering detail.

Attempts to simulate the above experiment with 0.24 D.S. xanthate resulted in mushy casts.

EXAMPLE 16 To 15 ml. of water added 0.439 g. (3 times stoichiometric amount) of butadiene diepoxide. Then weighed in 15 g. of an 11.10 percent sodium starch xanthate solution (0.44 D.S.), mixed well, and let set in a glass tube. Although the behavior of this reaction mixture and the casting was much the same as those of Example 12, the resulting dried cast was more shriveled, brittle, and fragile than those of Example 12. A

When this procedure was repeated with a 0.24 D.S. xanthate and 3 times thestoichometric amount of the diepoxide, a very brittle cast was also obtained.

Incorporation with Papermaking Pulp:

EXAMPLE 17 To 15 ml. of water added 0.50 ml. (0.55 g.) of 1,4- butanediol diglycidyl ether. The amount of the diepoxide is 3 times the stoichiometric amount of 1 mole of epoxide group per mole of xanthate group to be used. Then 15 g. of an 8.96 percent 0.24 D.S. sodium starch xanthate solution was weighed in and mixed rapidly until reaction was underway as evidenced by thickening and clouding. The mixture was set at room conditions for 1 hour, at which time it was a soft, yellow, opaque, slow-running gel. The gel was stirred into about 400ml. of water to disperse.

The dispersed gel was stirred into a 1,400 ml. suspension of unbleached, softwood, sulfat9e, papermakers pulp (30 g. of 75 percent moisture, 800 ml. SR freeness pulp, that had been soaked in ca. 600 ml. water and gently disintegrated in a Waring Blendor prior to final dilution).

The treated pulp suspension was set at room conditions for 3 hours, at which time the pulp had settled about one-third through the volume in the 2-1. beaker. Some clear water was decanted and then the beaker was inverted over a ;-inch mesh wire screen to permit drainage and formation of a thin mat. The mat was dried in the room air for several days. During drying and after drying, it was noted that the mat of treated pulp had a lighter hue and the surface appeared to have a denser or less-loose packing array of fibers than did a control mat made of untreated pulp in the same screen-forming technique. Also when dry, the treated mat was somewhat stiffer to hand. A portion of the dried mat was ground in a Wiley mill to 60 mesh and analyzed for sulfur content; found0.25 percent, d.b. This content represents ca. 13 percent retention of the added sulfurous derivative, after allowing for a blank sulfur content of ca. 0.10 percent in the pulp itself.

EXAMPLE 18 To 250 ml. of water added the same amounts of diepoxide and xanthate as in Example 17. Mixed well and set for 1 hour. A milky suspension developed. This was added to a suspension of paper pulp in the same manner as in Example 17 and another mat was formed.

The character of this mat was much the same as that formed in Example 17. The analysis of the ground mat showed 0.25 percent sulfur, d.b.., corresponding to ca. 13 percent retention of additive.

EXAMPLE 19 To ca. 1,400 ml. of water added the same amounts of diepoxide and xanthate as in Example 17. Let set at room conditions for 3 hours. The mixture became faintly turbid and a very small amount of solid sediment was noticeable on the bottom.

A 600-ml. suspension of the paper pulp prepared as in Example 17 was added. The mixture was set at room conditions for 3 hours and then a mat was formed. This mat was also much the same as the mat of Example 17. Analysis of a ground portion showed 0.23 percent sulfur, d.b., corresponding to ca. 13 percent retention of additive.

EXAMPLE 20 To 1,600 ml. of water added 15 g. of an 11.22 percent 0.22 D.S. sodium starch xanthate solution and 0.56 ml. (0.61 g.) of the diepoxide of Example 17. The amount of diepoxide is 3 times the stoichiometric amount of 1 mole epoxide group per mole of xanthate group. Mixed well and let set. By 7 hours a faint turbidity had developed. After 48 hours the turbidity was much more prominent and a fine precipitate was appearing. A 30-g. portion of the paper pulp, dispersed in 450 ml. of water, was stirred in and the mixture was processed into a mat.

EXAMPLE 21 To 15 ml. of water added 0.22 ml. (0.24 g.) of butadiene diepoxide and 15 g. of the same xanthate used in Example 17. The amount of epoxide is 3 times the stoichiometric amount of 1 mole of epoxide group per mole of xanthate group. The mixture was set at room conditions for 1 hour. The ensuing gel was much stiffer than that of Example 17 and would not flow. It was gently broken up in a Waring Blendor in ca. 400 ml. of water.

It was added to a pulp suspension as in Example 17. In

the 3-hour standing period, the pulp settled about one- In about 250 ml. of water 15 g. of the pulp described in Example 17 was soaked for an hour, broken up with a stirring rod, and gently beaten (to a small vortex appearance) in a blendor. Then 2.98 g. of a 10.91 percent 0.26 D.S. sodium starch xanthate solution was slowly added to the beating pulp and mixing carried on about 5 minutes more. Then 0.13 ml. (0.146 g.) of the diepoxide of Example l7 was added dropwise While beating and an additional 5 minutes of beating was accomplished. The suspension was transferred to a beaker to set overnight (16- 18 hours). In a matter of about 15 minutes a light, cloudy appearance developed in the suspension, without settling. The suspension was diluted to 800 ml. in a 1-liter beaker and formed into a mat. The mat was of noticeably lighter hue than a mat from an untreated pulp control. However, the determined sulfur content of the dried, treated mat indicated only a 7 percent retention of the treating product. The treated mat was somewhat stiflier to hand.

SERIES 2 minutes ex situ reaction, varied in situ reaction, 2.5 percent addition level, 0.26 D.S. sodium starch xanthate Breaking length, m.

Burst EXAMPLE 5 factor MIT fold Wet Dry This experiment was carried out in the same manner as Example 22 except that the diepoxide was added to 780 625 7,500 56. 2 560 620 7, 700 the beating pulp first, then the xanthate next. It was noted 980 645 8,730 that the whitening appearance took about 2 hours in the 260 155 6,350 setting step. Sulfur analysis indicated about 21 percent retention.

SERIES 3 18 hours in situ reaction, varied addition level, varied D.S., other additives Breaking length, Addition in. Xanthate, level, Burst MIT Additive D.S. percent factor fold Wet Dry Experimental 0. 57 10 60. 6 980 255 7, 790 Do 0. 26 10 66. 3 880 245 7, 980 0. 57 2. 5 54. 6 1, 000 220 7, 230 0. 2. 5 55. 5 590 225 7, 390 0. 10 2. 5 51. 1 500 200 7, 330 40.1 260 155 6,350 Gelatinized strach 2. 5 4 1. 9 350 175 6, 670 Na starch xanthate- 0.10 2. 5 42. 4 345 180 6, 480 Comm. cationic 2 r 2. 5 54. 2 715 130 s, 490

1 Gelatinized in same manner as used in making sodium starch xanthate with alkali. 2 A commercial catonic starch product normally used as a strength-improving paper additive.

EXAMPLE 24 Three series of trials embodying variations and combinations of the procedures of Examples 17-23 were established. The starch xanthates used were: 0 .10 D.S., 11.41 percent sodium starch xanthate; 0.26 D.S., 10.91 percent sodium starch xanthate; and 0.57 D.S., 11.16 percent sodium starch xanthate. The diepoxide was that of Example 17.

The variations in procedures Were as follows: Series 1 utilized a 5-minute ex situ (away from pulp) reaction between a given weight of the sodium starch xanthate solution and a given weight (3 times the stoichiometric amount) of the diepoxide in a weight of water equal to the weight of xanthate solution, followed by a 2-hour, unstirred, in situ (in presence of pulp) reaction of the ex situ reaction product after adding it to a 2-percent suspension (15 g. dry pulp in 750 ml. water) of pulp in a blendor with stirring. Series 2 was the same as Series 1 except that the length of the in situ reaction Was varied. Series 3 involved only a constant in situ reaction in which during the pulp agitation process in the blendor the xanthate was added to the pulp first and then the diepoxide.

In each Series the treated 2-percent pulp suspensions were diluted to 6,250 g. with Water (distilled used throughout), dropped to pH 7 with muriatic acid as needed, and processed into handsheets. The dried handsheets were tested for strength properties, according to TAPPI standard methods as follows:

Test: TAPPI Method No. Burst strength T 403 ts-63. Breaking length:

Dry T 494 os-70. Wet T 456 os-68. MIT fold T 511 su-69.

The results are in the following tables.

SERIES 1 5 minutes ex situ reaction, 2 hours in 1situ reaction, 2.5 percent addition eve Breaking length, m.

Bur

iactoi MIT iold Wet Dry I claim:

1. A method of preparing paper which comprises reacting a sodium strach xanthate having a xanthate D.S. of from about 0.1 to about 0.6 with an excess of an alkyl diglycidyl ether or an alkyl diepoxide in an alkaline aqueous solution, said excess being from 2 to 5 times the stoichiometric amount of one epoxide group per xanthate group in said sodium starch xanthate; adding the resulting reaction mixture to a papermarkers pulp suspension in amounts that results in levels of addition of from about 2.5 to 25 percent based on total weights of reactants and dry pulp; allowing the resulting pulp mixture to stand from about 0.5 to about 18 hours; forming water-laid paper from the pulp mixture; and drying said paper.

2. The paper prepared as described in claim 1.

3. The paper prepared as described in claim 1 in which the alkyl diglycidyl ether is 1,4-butanediol diglycidyl ether and the alkyl diepoxide is butadiene diepoxide.

4. A method of preparing paper which comprises reacting a sodium starch xanthate having a xanthate D.S. of from about 0.1 to about 0.6 with a 2 to 5 times excess of an alkyl diglycidyl ether or an alkyl diepoxide, based on the stoichiometric amount of one epoxide group per xanthate group in said sodium starch xanthate, in an alkaline aqueous solution in the presence of a papermarkers pulp in amounts such that the total weight of reactants is from about 2.5 to about 25 percent of the weight of the dry pulp; allowing the resulting reaction-pulp mixture to stand for about 0.5 to 18 hours; forming a water-laid paper from the reaction-pulp mixture; and drying said paper.

5. The paper prepared as described in claim 4.

6. The paper prepared as described in claim 4 in which the alkyl diglycidyl ether is 1,4-butanediol diglycidyl ether and the alkyl diepoxide is butadiene diepoxide.

References Cited UNITED STATES PATENTS 5/1968 Lancaster 162-175 X 8/1968 Bridgeford 260233.5 X

US. Cl. X.R.

162164, 183; 127-32; 260-9, 17.4 ST, BB, Cl, 233.3, 233.5 

